Cathode ray tube gun structure



1955 D. D. VAN ORMER 2,728,007

CATHODE RAY TUBE GUN STRUCTURE Filed July 1, 1953 2 Sheets-Sheet 1 INVENTOR.

flaw/ml. Vail firmer 495M LL 9 Dec. 20, 1955 D. D. VAN ORMER 2,728,007

CATHODE RAY TUBE GUN STRUCTURE Filed July 1, 1953 2 Sheets-Sheet 2 5'? gf 4 +2 0 my 1 6 g] 15 5 g a 44 40 fi INVENTOR.

United States Patent Oi CATHODE RAY TUBE GUN STRUCTURE David D. VanOrmer, Lancaster, Pa., assignor to Radio Corporation of America, acorporation of Delaware Application July 1, 1953, Serial No. 355,309

7 Claims. (Cl. 313-82) This invention relates to electron dischargedevices of the cathode ray type and particularly to mount structures andmeans to support electrodes in such devices.

The electron gun structure of cathode ray tubes convcntionally includesa cathode electrode, a control grid, an accelerating screen gridelectrode, and a second accelcrating electrode. These electrodes arenormally formed of tubular members which are mounted successively alonga common axis within a tubular neck portion of the cathode ray tubeenvelope.

The cathode electrode of such devices consists of a small tubularelectrode which is closed at one end and is mounted coaxially within thetubular control grid electrode. The mounting of the cathode electrode isa ceramic disc to which the tubular cathode is fixed through an apertureat the center of the ceramic disc. The combined ceramic disc and cathodeare mounted within the tubular control grid by locking the ceramic sothat the closed end of the cathode is at a predetermined distance fromone end of the control grid. The control grid at this end is closed by atransverse wall portion having a small aperture at its center alignedwith the closed end of the cathode. This end of the cathode is coatedwith an electron emitting material to provide a source of electronswhich are urged through the aperture of the control grid Theelectrostatic fields between these gun electrodes form the electronemission from the cathode into an electron beam directed substantiallyalong the axis of the tubular neck portion of the electron beam path andon the end wall or face plate of a larger bulbous portion of the tubeenvelope. Defiecting means are normally provided for scanning theelectron beam over the fluorescent screen in any desired manner, such asin a rectangular raster, for example.

The gun structure as described above is normally mounted within thetubular neck portion of the envelope by relatively heavy leads welded tothe metallic portions of the tubular electrodes and to metal pins scaledthrough the end of the tubular neck end, which are in turn connected tothe base pins of the tube. The structure thus described is of aconventional design and is well-known and is shown and described ingreater detail in U. S. Patent 2,496,127 to Joseph Kelar.

Similar structures are used in cathode ray tubes used in televisionviewing picture tubes. However, with the trend toward television picturetubes of larger fluorescent screen area, the tendency is to also extendthe length of the tubular neck portion of the tube envelope. However,the length of the front-to-back dimension ofthe cathode ray tube islimited from a practical standpoint by the size of the televisioncabinet in which the tube is to be mounted. It is desirable to keep thedimensions of such' cabinets, from front to back, as small as possibleso as to enable the cabinet to be passed through apartment-size PatentedDec. 20, 1955 ICC doorways, for example. Furthermore, a cabinet withsmall front to back dimensions is more desirable from an aesthetic pointof view. One solution has been in providing a larger deflection angle ofthe electron beam. However, another solution would also be to eliminatethe spacing between the gun and the stem of the tube, which is occupiedby the leads extending from the electrodes to the base pins of the tube.

Cathode ray tubes of the type described also have a relativelyinefiicicnt cathode structure. The cathode material on the closed end ofthe tubular cathode electrodes is normally heated to thermionictemperatures by a double helical filament coil threaded into the openend of the tubular cathode. During tube operation heat radiated from thecoil filament heats the tubular walls of the cathode electrode to atemperature atwhich sufficient heat is conducted by the cathode walls totheemitting end wall to provide a copious emission of electrons from thethermionic coating. Thus the cathode coating is indirectly heated byheat conducted to it by the side walls of the tubular cathode.Furthermore, the contact between the tubular cathode wall and theceramic support disc provides a loss of heat energy so that a cathodestructure of the type described uses an excessive amount of electricalenergy. Standard cathode filaments used in the tubes of the typedescribed require 0.6 ampere of current at 6.3 voltages or a heatdissipation of 3.78 watts. This amount of energy constitutes arelatively large drain of power from the circuit system of the tube. Itis desirable that such heater power he reduced to a minimum.

Cathode ray tubes of the type described also usev spacer elementsbetween the cathode supporting ceramic disc and the apertured closed endof the control grid electrode to provide the predetermined cathode-gridspacing. These spacers have taken the form of metal eyelets, annularceramic insulators or the like. If the cathode to grid distance iscritical, these spacers must closely conform by a small tolerance to thepredetermined spacing distance. This requirement necessitates closeinspection of each spacer and a process of matching spacers of a certainsize with cathode-ceramic assemblies of a specific size, since there arevariations both in the spacers and in the mounting of the cathode withinthe ceramic. Such a procedure of matching a spacer to a cathode-ceramicmember requires careful time consuming work.

It is, therefore, an object of this invention to provide a novel andsimplified electrode structure for a cathode ray tube.

It is a further object of this invention to provide a simplified andaccurate mounting structure for a cathode grid assembly in a cathode raytube.

It is another object of the invention to provide cathode ray tube havingshorter front-to-back dimension.

It is another object of the invention to provide a cab ode filament unitfor a cathode ray tube utilizing a mini mum of power output.

It is a further object of the invention to provide a cathode-gridassembly utilizing a simplified and accurate mounting structure.

The invention is in the structural design of a cathode control grid andaccelerating grid assembly. The novel assembly comprises a supportingtubular accelerating electrode in which a pair of parallel disposedsupport plates of an insulating material are locked in place. Betweenthe supporting plates there are fixed a control grid elec- Figure 1 is apartial sectional view of a cathode raytube in accordance with theinvention.

Figure 2 is an enlarged sectional view of part of the gun structure ofthe tube of Figure 1.

ama qo-v 3. Figure 3 is a cross sectional view along lines 3--3 ofFigure 2. v

Figure 4 is a sectional viewl of part of the structure of Figure 1- atright angles. to the section; of Figure 1-.

FigureSisa sectional view of: a simplified gunstruc: ture utilizing adifferent form. of the invention;

Figure l discloses a cathode ray tube whichmaybe used for-televisionviewing. The tuheconsistsof an.

evacuated :envelope having a large :bulbousshell orconelike portion. 10.and a. tubular neck portion 12 fixed to the bulbousportion. Withinthe'tubular'neelc12"is'mounted an electron gun 14- for. forming-anddirecting-a=beam of electrons substantially alongthe 3 axis of -the neckportion 12-toward a fluorescent screen 16 formed on the-inner' surfaceof the end-wall face plate 18- of the bulbousenvelope portion 10;

Two pairs of'coils are formed into a neck yoke '24).

mounted on the envelope neck 12 for scanning the. electron beam in anydesired'pattern over the surface of the fluorescent screen 16. Thescanning coils are conventionally arranged withthe coils of'eachpairconnectedin a seriesandmounted on opposite sidesof the tubularv neck12'; Each pair ofcoils is connected to appropriate sources of saw toothcurrents for providing the scanning fieldsto move the electron beaminthe desired raster pattern over the fluorescent screen 16. Afocusingcoil 22f may be used to focus the electron beam to a; fine/spoton he. fluor scent Screen u n be. op on.

The electron gun of conventional cathode ray tubes normally consists ofa plurality of tubular electrodes. The cathode of the gun comprises asmall tubular electrode having. one end closed by asolid wall portionupon which is formed a coating oflelectron emissive material such asarnixtnre of barium andstrontium carbonates.

The .tubular cathode is mounted Within a tubular control grid whichisclosedjatone end'by a solidwall'having a small aperture at its center.with the. coated end-wall of the cathode closely spaced from andalignedwith the central aperture of the control" grid, The gun alsoisnormally formed with a'plurality of tubular accelerating electrodesspaced along a common axis and'having apertures therethrough alignedwith the central aperture of the control grid for the,passagetherethrough of thelelectrons from the cathode in the formof a beam.Electron guns of this type are shown and de scribed patent'to J; Kelar2,496,127;

In accordance with. theinvention, however, the'clectron' gun 14 isprovided With-a simplified andmovehelectrode arrangement. As shown inFigures 2, 3, and 4; thecathode electrode consists of a tubular member24 which is mounted on and extends between two parallel sheets" of mica26: Furthermore, the'tubular cathode 24"is en-' closed in an openended'box construction 28 having at the box b'y the two mica plates-26.

The mica grid assembly 26 -2 8 -'is; mounted "within a tubularaccelerating electrode 32 Ametaidiaphragm or walljportion-34 is fixedbywelding, for example; across one end of the tubular acceleratingelectrodo 32'as shown in Figure 2. The diaphragm 34 iis'spaced' asutlicient'distance from the'adjacent end oftubular member' 32"to.

pr v de. a ap-l ke. streams.atth tend AS shown in ure. he .mi anl tes.2.65am. ,i.1m-:n

snedsqtha ti thex arefix sttd th t i nfir ture 28, they will sliptightly into;.thegtuhnlat ,electitode.

'Ihe cathode is mounted.

greater detail; for example; in the above cited The assembly forms 32 torigidly hold the mica-grid assembly 2628 within the tubular member 32and will prevent lateraldisplacement of the assembly within the tubularmember 32. A retainer ring 36 is slipped into the open end of thetubular member 32 and into engagement With the adjacent ends of the micasheets 26 at which point the ring 36 is Welded or locked by other meansto support member 32 to hold the grid-mica assembly 26-28 in positionand to prevent any axial movement thereof.

Opposite side Walls of tubularmember 32. are cut away: as shownatS S,for example on both sidesandinali'gnment with the ends of the tubularcathode 24. The openings 38 allowthe mounting of the cathode 24- intothe mica-grid assembly after the assembly: has been fixed within thetubular accelerating support member 32. Cathode 24 is mounted inopenings punched through mica sheets 26 to fit cathode 24 tightly. Alsothe openings 3.8.permitpassing of lead 40,.toithev cathode 24.. Withinthe. tubular. cathode 24. there. is positionedv a folded. filae mentarycathodefilament 44.for raising the. temperature.

of. the cathode to thermionictemperatures. The leads 46 of the cathodefilament 44 are also broughtout of one.

ofthe. openings 38 in member 32 and ftxedto. appropriate basepins 48extending through the pressor. closedv end 47 of the tubular neckportion 12., A- lead 42fpasses. through a centralopening in retainerring 3.6, tothe. con:

trol grid box 28. Cathode andgrid leads. 40and'42 arealso fastened toother base. pins 48 respectively. The pins 48 extendthrough the press 47and are connected to pins. 49 fixed into the tube base 50.

The outer surface of the, tubular cathode electrode124.

is. coatedjwith electron emitting materialsuchas a mix: ture of bariumand. strontium carbonate to. provide. a sOl fce of electrons within thetube. Aligned with a. coatedsurface of cathode 24there is an aperture52..in. the top of the grid. box 28. to provide passage. therethrough ofelectronsfrom'the cathode surface. accelerating electrode diaphragm 34also has formed at its .center an aperture 54in alignmentwithapertureSZI and the coated cathode surface.

Spaced alongthe axis of tubular member 32-is a second tubularaccelerating electrode 56. for providing a high, positive potentialgradient in. the beam, path and. to.. accelerate the electrons emitted.from cathode. 24 'to. high velocities. Tubular electrode.5.6is. closedat its opposite. end-by an apertured diaphragm. or: wall portion 58Mounted. at the edges of thediaphragrnSB are spring fingers or spacers60 for positioning the end'ofithe. accelerating electrode 56 on the.axis of the tubularneck portion 12; Also the spring fingers60jmake'electri c'alj contact. between electrode, 56 and a conductive.wall coat; ing 62extending from the end of {electrode v56 to a.ppi ntadjacent the fluorescent screen 16of the tube. i

The operationv of the tube is that in,whi ch current.

passing through filament 44 heats tubular cathode 24' to a temperatureat which electrons are freely emitted from the cathode coating. Thecontrol grid electrode 28 is normally. operated; at a. range ofpotentials negative to.

the potentialof the cathode 24. The accelerating elecnode 32, however,isoperated at a potential of'several' hundred volts positive to cathode24, while electrode 56 is'operated'at .the highest potential inthe orderof ',from.

1"to' .18,QOQ volts depending upon the use andi'sizegof' the cathode raytube. As is well known, thenegativev potential of electrode 28'can bevaried until the positive accelerating'potential of electrode 24 willextendthrough aperture 52 and pull electrons emitted from thecathode'coating through aperture 52. These electrons are'a'cceleratedihroughaperture 54 into thetubular electode 56."

The difference in potential between electrodes'32'and' 56 provideselectron lens field which aidsij forrning he le tr nsintoa eam. Thebeamelectrons, h ve re .dixe g ng in. thei pa ge ro gh the tubular.

' electrode 56;. The field.of.the.focusing,coil,.22.pIOvideaamonuergingaction. onelectrons of the .beamand causes;

The.

them to converge or become focused to a small welldefined beam spot onthe surface of the fluorescent screen 16. The voltages shown in Figure 2represent those which have been applied to the respective electrodesduring successful operation of a tube of the type described. However,these values'need not be limiting.

The adjacent ends of electrodes 32 and 56 are cut at an angle to thecommon axis of these electrodes, as shown in Figure 2. This has theeffect of tilting the lens field between electrodes 32 and 56 so thatthe beam electrons passing into this field are bent from their axialbeam path in the direction of the axis of the tubular envelope member12. A magnet 66 mounted on the tubular neck portion 12 provides amagnetic lens field for bending the beam back onto the axis of the neck12 and to direct the beam through the apertured diaphragm 58 at the endof the tubular electrode 56. The arrangement provides a means fortrapping the negative ions formed within the electron beam. This doesnot constitute a part of the invention and is more fully described inthe copending application of L. E. Swedlund, Serial No. 130,775 filedDecember 2, 1949. Furthermore as part of the ion trapping arrangement,the electrodes 32 and 56 mounted on a common axis are inclined at asmall angle to the axis of the tubular neck portion 12.

The novel electrode mounting arrangement, as described above andconsisting of electrodes 24, 28 and 32 provides an assembly which can beboth simply and ac curately made. Mica can be accurately cut and punchedto very close tolerances. Accordingly, mica plates 26 can be accuratelycut to provide the correct spacing between cathode 24 and the controlgrid aperture 52 to Within very close limits. Furthermore, the spacingbetween the control grid aperture 52 and the accelerating diaphragm 34can be accurately maintained from tube to tube and within the requiredlimits. Thus the assembling of the electrodes 24 and 28 to the micaspacer elements 26 can be done easily and accurately. The mounting ofthis cathode grid assembly within the accelerating electrode support 32can be accomplished easily and without any loss of accuracy in electrodespacing.

By bringing the leads 40 and 46 of the respective electrodes through theside wall of support electrode 32, it is possible to mount the electrongun 14 closer to the press 47 of the tube. This results in a shortertube neck, which is of an advantage in large tubes where thescreento-stem dimension becomes critical.

An additional advantage of the structure described is the ability to usea filamentary folded heater within the cathode 24 in place of thereverse wound coil heaters conventionally used. The difficulty of usinga tubular cathode having the emitting surface on a closed end of thecathode, as described above, is the necessity of using an excess amountof power in order to raise the temperature of the tubular cathodesufiiciently high to heat the coating at the closed end to thermionictemperatures. However, the structure shown in Figures 2 and 4, forexample is that in which the filament 44 is in direct con tact with thecathode Wall upon which is coated the thermionic material. This providesa much more ei'ficient manner of heating the electron emitting coatingand enables the use of a much less power. Furthermore, there is littleloss of heat to the mica supports 26, as was true with the conventionaltype cathode mounted in a heavy ceramic near the emitting end thereof.

The electrode 28 may be formed as a single piece and wrapped around toform its boxlike structure. The bottom of the box or the side 29 ofelectrode 28 opposite from the grid aperture 52 forms a light shield toprevent a light from the heated cathode 24 from being directed onto theglass surfaces of the press 47 and in turn being reflected down the tubeneck 12 onto the fluorescent screen 16. Grid 28, however, need not bemade from a single piece wrapped into the desired shape, but may be madeof a plurality of metal sheets if desired.

Figure 5 shows an adaptation of the invention of Figure 2 in which somefeatures of the invention can be used in a triode type cathode ray tube.In Figure 5, the mica sheets 26 are locked together by metal plates 68and 76 on the top and bottom respectively and by side plates 72, ofwhich only one is shown. The tabs 74 corresponding to tabs 30 of Figure2, for example, extend through the micas 26 from each of the electrodeplates 68, 70 and 72 and are bent or twisted to rigidly lock the plates6S, 7% and 72 to the mica sheets 26 to form a rigid box structure. Acathode 24 of the type described in Figures 2 and 4 is mounted in asimilar manner through the mica strips 26 and has its outer surfacecoated with an electron emitting material. The coated surface of cathode24 is mounted in a predetermined spacing from an aperture 76 in plate68. This cathode-grid-mica assembly is mounted on base pins 48 bywelding the pins 48 directly to the plate structures of the assembly andalso by the leads 75 which extend from the filament 44, the cathode 24and plate 68 to the several base pins 48. The accelerating electrode ofthe tube of this type consists merely of wall coating 60 which isextended down the neck 12 of the tube envelope to overlap the grid plate68. The operation of the tube is of the type disclosed in the abovecited application to L. E. Swedlund.

While certain specific embodiments have been illustrated and described,it will be understood that various changes and modifications may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electron gun for a cathode ray tube, said electron gun comprising,a tubular electrode, a pair of support members of electricallyinsulating material supported within said tubular electrode, a tubularcathode electrode supported Within said tubular electrode transverselyto the axis of said tubular electrode and by said insulating supportmembers, and an apertured plate electrode supported by said insulatingsupport members within said tubular electrode and adjacent said cathodeelectrode.

2. An electron gun for a cathode raytube, said electron gun comprising,a tubular electrode, a first apertured metal plate member fixed Withinand transversely across said tubular member, a pair of support membersof electrically insulating material mounted within said tubularelectrode on opposite sides of the axis thereof in contact With saidtransverse metal plate member, a tubular cathode electrode supportedwithin and transversely to the axis of said tubular electrode and bysaid insulating support members, and a second apertured metal platemember supported within said tubular electrode by said insulatingsupport members between said cathode electrode and said first metalplate member.

3. An electron gun for a cathode ray tube comprising, a tubularelectrode, a first apertured plate member fixed within and closing saidtubular electrode adjacent one end thereof, a pair of support plates ofelectrically insulating material mounted within the other end of saidtubular electrode and facing each other on opposite sides of the axis ofsaid tubular member, an edge of each of said insulating support membersin contact with said first apertured plate member, a tubular cathodeelectrode supported within and transversely to the axis of said tubularelectrode by said insulating support members, and a second aperturedmetal plate member fixed within said tubular electrode to saidinsulating support members between said cathode electrode and said firstmetal plate member, said first and second metal plate members eachhaving an aperture therethrough on the axis of said tubular members andaligned with a surface portion of said cathode electrode.

4. An electron gun for a cathode ray tube, said electron gun comprising,a tubular electrode, a pair of support members of electricallyinsulating material supported within: saidtubular electrode, a: tubularcathode electrode supported within: and transversely to the axis oi saidtubular; electrode: and by said insulating support members; and? anapertured platev electrode supported withinsaid. tubular electrode bysaid insulatingsupport-mem hers adjacent said cathode electrode, saidtubular electrodezhayingz an aperture in the side Wallthereofiandleadmembers connected to one of said electrodes Withinsaiditubular memberand passing through said-aperture inztheside'wallthereof.

5". electron: gun fona cathode ray tube, said elec-' tron; gumcomprising, a tubularelectrode, a first apertured; metaliplate memberfixed within and transversely across said tubular: member, a pairofsupport mernbers of: electrically insulating material mounted withinsaid tubular electrode-on opposite sides of the axisthereof in'scontaetwith said transverse metal plate member, a tuhulari cathode electrodesupported Within and transversely tOithC axisof said tubular electrodeand by said: insulating support members, anda second aperturedmetakplate-membersupported within said tubular'eleo trode.bysaidinsulating support'members between said cathode; electrodeandisaid'first metalplate-member, said' tubular electrode having anaperture in the side wall thereof and lead members i connected :to oneof said-electrodes within said tubular member and passing-through saidaperture in the sidewall thereof.

6. An electrongun for a cathode ray tube'compris inggatubular electrode,a plate member fixed within andclosin'gzsaid' tubulari electrodeadjacent one endthereof, said plate member having an aperturetherethrough, a pair'of support plates of electricallyinsulating'material mounted within the other end of said tubularelectrode andzfacing. each other on opposite sides of the axis of saidtubularmember, anedgeof each of-said insulating support members incontact with said first apertured plate member, a tubularcathodeelectrode supportedwithin and transversely to the axis of said' tubal-anelectrodeby: said insulatingsupport members,- and a second tubularmetalmemberfixed within said'tubular 'electr'ode between said insulatingsupport members and enclosing said tubu' larcathodeelectrode, saidsecond tubular member hav ing an aperturetherethrough between a surface"of; saidcatliode electrode and said aperture'in said plat'e member.

7. An electron gun-tor a cathode ray tube, said elec-' tron guncomprising, a tubular electrode, a metalplate' member'fixed within andtransversely across said tubular: member," saidplate member havinganaperture there tl1rough,:a pair: of support members of electri'callyinsu-' latingmaterial mounted within-said tubular electrode on oppositesides of the axis thereof in contact with said transverse metal platemember; atubular'cathode electrode supported Withinandtransvers'ely tothe a'xisof-said tubularelectrode and by said insulatingsupport members,and-a second tubular'metal electrode member supported: within: saidtubular electrode between said insulating support members and enclosingsaid cathode: electrod'e, said second tubular electrode member having-anaperture through thei wall=thereof aligned with said aperture in saidmetal plate member a-nd a surfac'e'portion of said tubular cathodeelectrode; said cathode surface portion having a coating of 'therm-ionicemitting -materialthereon.

References Gited inth'e fileiof this-patent UNITED STATES PATENTS2,194,547 Haines 'Mar. 26; 1940: 2,223,908 Bull- Dec. 3, 1940 2,231,961Soller -Feb'. 1 8, 1941 2,268,196 Pierce Dec, 30, 1941 2,496,127 Kelar aJan. 31, 1950 2,516,752 Carbrey July 25, 19'50

